Hydraulic hold-down



Fgb. 16, 1943. L. R. WILLIAMSON HYDRAULIC HOLD-DOWN Original Filed Jan. 9, 1959 INVENTOR. LARKIN 'R WlLLlAMSON BY J I ATTORNEYS Patented Feb. 16, 1943 2,311,147 HYDRAULIC HOLD-DOWN Larkin R. Williamson, Brooklyn, N. Y., assignor to E. W. Bliss Company, Brooklyn, N. Y., a corporation of Delaware 7 Original application January 9, 1939, Serial No.

249,890, now Patent No. 2,269,328, dated January 6, 1942. Divided and this application August 14, 1941, Serial No. 406,829

4 Claims.

This invention relates to hold-down mechanism and particularly to a hydraulic hold-down system adapted for use in holding a plate or sheet whilethe same is acted upon by a tool. More specifically, my invention is directed to such a hold-down mechanism in connection with a power shear. This application is a division of my application Serial No. 249,890, filed January 9, 1939, which has resulted in Pat. No. 2,269,328, Jan. 6, 1942.

Hydraulic hold-down systems in general are not new but insofar as I am aware have always been subject to various disadvantages. Among other imperfections these prior devices have been subject to leakage at the hold-down proper, whichresulted in gumming the work and requiring a cleaning operation after the piece Was sheared. It is the main object of this invention to meet this drawback by providing a novel form of hold-down by which any leakage is prevented. A further object has been to provide a system in which variation in the fluid pressure in the line is automatically compensated for by the pump. Other objects of the invention will become apparent from the specification, drawings and claims. To the accomplishment of the foregoing and related ends, said invention, then, consists of the means hereinafter iully described and particularly pointed out in the claims; the annexed drawing and the following description setting forth in detail certain mechanism embodying the invention, such disclosed means constituting, however, but one of various mechanical forms in which the principle of the invention may be used:

In said annexed drawing:

Fig. 1 is a front elevation of a shear employing my hold-down; and

Figs. 2 and 3 are sectional views of the holddown proper and pump respectively.

Referring now to Fig. 1, I use my mechanism in conjunction with a power shear employing the usual side plates l0, bed I2 and ram or slide M, which carries the movable knife. The ram is driven by a suitable motor l5 acting through belting IT to drive a pulley [8. A gear of this pulley 18 engages a drive member of a clutch 20 and continuously rotates such member. The clutch 20 which may be of any type Well known in the art, is hydraulically operated to couple the motor l5 operatively through mechanism to reciprocate the ram I4.

A series of hold-down members 22 is carried by the shear immediately in front of the ram and is preferably secured to the same.

Said holdl down members are adapted to engage work resting on the bed l2 to secure the same against displacement upon descentof the ram I 4 and its associated shear knife.

These hold-down members, as shown in Fig. 2,

each comprise a cylinder 24 and a piston 25, the lower end of which engages the work. The upper end of each piston is shaped substantially like a bowl as shown in Fig. 2 and is provided with a cap 26 to'secure a packing diaphragm v28 to the piston. The diaphragm is made'of an oil resistant, resilient material such as neoprene. The inner part of the diaphragm has the same shape as the piston with edge portions embracing the piston edges. The outer part is shaped like a flange. This outer annular portion of the diaphragm is sealed against the cylinder 24 by a cylinder cap 3!] suitably bolted thereto as at 32. Oil, as hereinafter described, is admitted to the chamber 33 to actuate the hold-downs, whichare normally held retracted by springs 34 interposed between the cylinder and'the piston. A stop 35 prevents cap 25 from being pressed too far against cap, 30 and from taking up the room in the chamber 33 which the oil is supposed to fill. The particular formation of diaphragm 28, reminding of corrugated metal, insures a great flex-.- ibility and makes it possible that the packing closely follows the movements of piston 25, when the same is pressed down by oil from chamber 3'3. The several hold-downs, as shown in Fig. 1, are connected to a unit to be operated from a single fluid line. The clutch which controls the driving of the ram is likewise hydraulically operated and is actuated by the admission ofoil 'under pressure from a side line.

The pump for supplying oil under pressure to operate the clutch line and the hold-down line is indicated generally at 42 in Fig. 1, and best shown in Fig. 3. This pump is driven from the shaft of the clutch 29, which shaft drives a connecting rod 44 at the end of the shaft, which is pivoted as at 45 to a piston plunger comprising two parts 41 and 49. These two parts are normally maintained separate from each other by a strong compression spring 59, but are limited in their movement apart by a central bolt 52 engaging the parts 41 and 59. The part 49 is close- 1y fitted into a cylinder 54 and reciprocation in this cylinder builds up the necessary oil pressure in line 55, which supplies the working parts of the unit.

From a description of the pump it will be seen that I have incorporated mechanism therein to very simply control the operation of the pump is at a predetermined value, which is equivalent to or slightly greater than the compressive strength of the spring 50 the part 49 of the pump will remain idle and the part 41 will continue movement, acting only to compress thespring. By this construction a pump is provided which is continuously driven, but the effective operation of which is controlled by the pressurein the line.

1 shearing means and hydraulic hold-down means for clamping work in timed relation with said shearing means, clutch mechanism to connect aid shearing means to a driving means and a The pump supplies the line 55 which, at one side passes through a check valve 51 and leads to two double acting valves which control the admission of oil to the hold-down line and the clutch operating line. These parts are not shown because they do not form a part of the present invention. The check valve 5! acts to maintain the pressure at said valves and prevents its fall each time the member 49 is raised to increase the effective volume of the cylinder 54. The other side of the line 55 leads through a second check valve 58 to an oil reservoir and this valve is mounted to prevent transmitting the built-up fluid pressure into the reservoir, but will permit oil to be sucked into the line 55.

In operation a workman first places a sheet of material on the bed l2, then actuates a mechanism to admit oil under pressure to the holddown chambers 33, whereupon the hold-downs proper 25 clamp the work to the bed. As soon as the piece is clamped in the proper position pressure is admitted to the line for engaging the clutch and thus for reciprocating ram H to shear the work.

. Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the structure herein disclosed, provided the means stated by any of the following claims or the equivalent of such stated means be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In a hydraulic hold-down a plurality of cylinders; each comprising a piston responsive to fluid pressure, said piston having a concave top, a diaphragm shaped snugly to fit said top and having side portions laterally enclosing said top and extending radially covering the upper end of the wall of said cylinders, a cap on top of said diaphragm shaped to fit the contour thereof,-a

fluid system under pressure to control said holddown and said clutch mechanism, the combination of a plurality of hold-down cylinders each comprising a piston responsive to fluid pressure and adapted alternately to grip and release said work, aid piston having a concave top, a diaphragm shaped snugly to fit said top and having side portions laterally enclosing said top and extending radially covering the upper end of the walls of said cylinders, a cap on top of said diaphragm shaped to fit the contour thereof, a second cap for sealing the flanges of said diaphragm to the ends of said cylinder walls, a spring in said cylinders normally holding the piston in retracted position and means for holding said first mentioned cap against displacement.

3. In a hydraulic hold-down with a plurality of cylinders, in combination a piston responsive to fluid pressure in each of said cylinders, said piston having a bowl-shaped top, a diaphragm shaped closely to embrace said top, flanges on said diaphragm extending over the upper end of said cylinders, means for holding said diaphragm against displacement and a pump to build up pressure in said fluid, said pump comprising a two-part piston, a rigid member for limiting the movement of said piston parts apart from each other and a calibrated spring for maintaining said two piston parts separated, said spring upon being deformed allowing one of said piston parts to function independently of the other thereby terminating the pump action.

4. In a hydraulic hold-down with a plurality of cylinders, each comprising a piston responsive to fluid pressure, in combination a pump to build up pressure insaid fluid, said pump comprising a two-part piston, a rigid member for limiting the movement of said piston parts apart from each other, a calibrated spring for maintaining said two piston parts separated, said spring upon being deformed allowing one of said piston parts to function independently of the other thereby terminating the pump action.

LARKIN R. WILLIAMSON. 

